Circuit for starting and operating discharge tubes



Oct. 30, 1962 M. SPECTOR 3,061,759

CIRCUIT FOR STARTING AND OPERATING DISCHARGE TUBES Original Filed June27, 1951 INVENTOR. Morris Specfor Unite States 3,061,759 CIRCUIT FORSTARTING AND OPERATING DTSCHARGE TUBES Morris Spector, Highland Park,lill., assignor to Advance Transformer Chicago, EL, a corporation oflilinois Original application .lune 27, 1951, Eer. No. 233,850. Di-

vided and this appiication Aug. 20, 1957, Ser. No.

6 Claims. (Cl. 315-257) This application is a division of my pendingapplication, Serial No. 233,850 filed June 27, 1951, and issued asPatent No. 2,848,652 on August 19, 1958.

This invention relates to circuits for starting and operating one ormore discharge tubes of the hot cathode or cold cathode type.

There has recently been developed a ballast for starting two dischargetubes in sequence and thereafter operating them in series. Because thetubes are started in sequence the ballast need supply the startingvoltage for only one of the tubes at a time, whereas in a two tubeseries circuit if the tubes were to start at the same instant theballast would have to supply double the open circuit starting voltagerequired for a single lamp. Because of the sequential starting the highstarting voltage is applied first to one end and then to the other glowdischarge lamp. The time lapse in the sequential starting is so slightthat it is not noticeable and the lamps appear to start simultaneously.It is one of the objects of the present invention to provide a new anddesirable circuit for a ballast of the above type which will start twolamps in sequence and then operate them in series.

It is a further object of the present invention to provide a new anduseful circuit for starting and operating even one lamp and wherein theportion of the ballast circuit that is used to provide the high startingvoltage is to all intents and purposes out of the circuit during theoperating time. Since it is in circuit for only a negligibly smallproportion of the total operating time the output efliciency of thatportion of the ballast is not important and therefore that portion ofthe coil may be made of very fine wire, thereby reducing the amount ofcopper used and, in many instances, also reducing the amount of ironused in the ballast.

The attainment of the above and further objects of the present inventionwill be apparent from the following specification taken in conjunctionwith the accompanying drawing forming a part thereof.

In the drawing:

FIGURES 1 through 4 are circuit diagrams illustrating differentmodifications of the present invention; and

FIGURE 5 is a plan view of one form of ballast suitable for use with thecircuits of the present invention.

In FIGURE 1 there is shown a circuit for starting and operating two glowdischarge devices, which in this instance are fluorescent type instantstart cold cathode lamps L and L by means of a ballast that includes aprimary P, a secondary S and another secondary S The ballast may be of aphysical construction such as shown in FIGURE 2 or 3 of the applicationof Albert E. Feinberg, Serial No. 135,669, that issued as Patent No.2,558,293 the 26th day of June, 1951, to which reference may be had fora more complete description of the physical structure of the ballast. Itis SllffiClCl'lt here to state that the ballast is a shell type ironcore on which the three coils P, S and S are mounted, the secondariesbeing physically at opposite ends of the core with the primary betweenthem. A magnetic shunt 1G is provided between the primary and thesecondary S and a similar magnetic shunt may be provided between theprimary and the secondary S the magnetic shunts including Patented Oct.30, 1962 air gap. The windings S and S have a high leakage reactance andboth are loosely coupled with the primary, but the secondary S is moreloosely coupled to the primary than is the secondary S The primary andthe secondaries are so electrically connected that when alternatingcurrent voltage is supplied to the primary the relative directions ofthe induced open circuit voltages in the primary and secondaries S and Sare as shown by the arrows '11, 12, and 13, respectively, namely, thedirection of the secondary voltage S is the same as that of the primary,whereas the direction of the induced voltage of the secondary S isopposite that of the primary.

The lamp L is connected in series with a condenser 20 across the primaryand the secondary S the secondary S being, during the open circuitcondition, in step-up autotransformer relationship with the primary.

The instant that voltage is applied to the primary the combined voltagesof the primary and the secondary are available to start the lamp L Onthe other hand, at that instant the total voltage applied to the lamp Lis the voltage of the primary plus the voltage of S minus the voltage ofS This is insufficient to start the lamp L The lamp L starts. Thecondenser is of smaller capacity reactance than the inductive reactanceof the circuit including the primary, the secondary S and the lamp L sothat current flowing in this lamp circuit is lagging. As soon as thislamp starts and current commences to flow through the secondary S thehigh leakage reactance of the lagging current secondary S inducestherein a voltage having a component in a direction substantiallyopposite the direction indicated by the arrow 12. At this instant thevoltage now applied to the lamp L is the sum of the voltage of S plusthat reverse component of S minus the voltage of P. This is sufficientto start the lamp L Once the lamp L starts, the lamp L having alreadystarted, the two lamps L and L operate in series with the condenser 26and are supplied with operating current by the secondary S FIGURE 2shows an alternate circuit wherein the lamp L in series with thecondenser is connected directly across the secondary winding S whereasthe lamp L is connected across the secondaries S and S in series. Duringstarting the lamp L has an initial voltage applied thereto equal to thatof S This is sufficient to start the lamp. The lamp L has a voltagethereacross which is the difference between the voltage S and thevoltage of S That is insuificient to start the lamp. Immediately uponstarting of the lamp L current commences to flow through the coil S Thiscurrent is a lagging current because the reactance of the condenser 20is chosen of such a value as to be less than the inductive reactance ofthe secondary S The lagging current flowing through S induces therein avoltage having a component substantially opposite to that indicated bythe arrow 12. The voltage across the lamp L is now the sum. of thevoltages of S and S and that is sufiicient to start the lamp L Once thelamp L starts current then flows through both lamps in series, theseries circuit including the lamp L condenser 20, secondary coil S andthe lamp L The secondary S is at this time shunting the lamp L and thecondenser 2th Due to the high leakage reactance of the secondary Snegligible current flows through the secondary S In the circuit ofFIGURE 3 the primary P is connected across a source of volt 60 cyclealternating current as before, the lamp L in series with the condenser20 is connected across the secondaries S and S and the lamp L isconnected across all three of the windings. The connections are suchthat when alternating voltage is applied to the primary P and when thelamps L and L are out of the circuit the voltages induced in thesecondaries S and S are always in the same direction, which is adirection opposite that of the direction of the voltage of the primaryP, as indicated by the arrows 11, 12 and 13, which indicate the relativedirections of the voltages when the lamps L and L are open circuited.This means that the voltage across the ballast is the difference betweenthe line voltage and the sum of the voltages across S and S ,Thisvoltage is insufficient to start the lamp L The sum of the voltagesacross the secondaries S and S is sutlicient to start the lamp L Thecondenser 20 is of a capacity less than the inductive reactance of thesecondaries S and S so that the current flowing is lagging. This inducesin the secondaries S and S a component voltage opposite to thatindicated by the arrows l2 and 13 or in the same direction as thatindicated by the arrow 11. This is sufficient to start the lamp L Oncethis lamp starts current thereafter flows through the lamp L condenser2d and lamp L in series, this series circuit being connected across theprimary P, which has the line voltage applied thereto. This voltage issufiicient to maintain both lamps operating. At this time the windings Sand S shunt the lamp L in series with the condenser 20. Due to the highleakage reactance of the secondary S negligible current flows throughthe shunting circuit.

In the description of FIGURE 3 it is noted that S and S are connected inseries. It is thus possible to combine the coils S and S to constitute asingle high leakage reactance coil. It is also possible to maintain thetwo coils S and S physically separate, as shown in the above referred toFeinberg patent, and as illustrated in FIGURE 3, and making the leakagereactance f the two coils such that when current commences to flowthrough the lamp L there will be a reversal of voltage in only one ofthe two coils S S As a result, after the lamp L starts, the resultingvoltage that is applied to the lamp L is the primary voltage plus thedifference between the voltages of the secondary S S For instance, ifthe coil S is the one which due to its leakage reactance produces uponthe commencement of flow of lagging current therethrough a voltagecomponent opposite to the component indicated by the arrow 12, then thecoil S is made of many more turns than the coil S so that its voltage isof the order of twice that of the coil S The arithmetic sum of thesevoltages as applied during the instant of starting of the lamp L issufficient to start that lamp. The difference of these voltages, afterstarting of the lamp L added to the voltage of the primary P issuflicient to start the lamp L After starting of the lamp L both lamps Land L and the condenser 2t operate in series from the voltage of theprimary P. The shunting circuit across the lamp L and the condenser notonly has a high leakage reactance to limit the current flow therethroughbut the voltages of the two coils S and S are bucking, thereby furtherlimiting the flow of current therethrough.

FIGURE 4 shows another modification of the present invention. In thisinstance the lamp L and the condenser Ztl are connected across thesecondary S which is of sufficient number of turns to provide asufiicient voltage for starting the lamp L The condenser 20 is of acapacity reactance less than the inductive reactance of the winding Splus the lamp L so that the starting current flowing through the coil Sis lagging. The voltage across the transformer when the lamps L and Lare open circuited is the sum of the voltages of the primary or linevoltage plus the voltage of the secondary S minus the voltage of thesecondary S This is insufficient to start the lamp L which is connectedin series with a choke 34 After starting of the lamp L the laggingcurrent flowing through the winding S produces a reverse component ofvoltage therein which is now additive to the voltages of the primary Pand secondary S and is suificient to start the lamp L The lamp L inseries with. the choke lights. Once this happens a circuit is formedincluding the lamp L choke 30, condenser 20 and lamp L in series,connected across the primary P and secondary S in series. The primary Pand secondary S are in step-up auto-transformer relationship. Thesecondary S at this time shunts the lamp L and condenser 29. Due to thehigh leakage reactance of the secondary S this shunt circuit takes anegligible current. The choke 39 is a conventional iron core choke suchas is commonly used in fluorescent lamp circuits. It may comprise, forinstance, an E-shaped magnetic core having a winding it) on the centerleg and a bridging bar or iron extending across the three legs of the Eto complete the magnetic circuit.

In each of the circuits above described there is shown an arrangementfor starting two glow discharge lamps in sequence and operating them inseries. Each of the circuits is operative for controlling a single lampif desired. in such case the respective circuits are used for operatingthe lamp L the lamp L being omitted and, when omitted, being replaced bythe equivalent of a short circuit across the terminals of the lamp LThus, in FEGURE l the condenser 2t? would be connected directly acrossthe primary P and secondary S In FIGURES 2 and 4 the condenser 2d wouldbe connected directly across the secondary 5 whereas in FIGURE 3 thecondenser Zl would be connected directly across the secondaries 8 -8 inseries with one another. In each such circuit the operation would be aspreviously explained, that is, when line voltage is applied it firstinduces a current flow through the condenser 20 in series with itsassociated coil S The current is a lagging current because the capacityreactance of the condenser 20 chosen is less than the inductivereactance of the circuit which includes the condenser, and the laggingcurrent results in a reverse component of voltage in the secondary SThis then provides a sufficient voltage for starting of the one lamp LUpon starting of the lamp L the condenser Ztl operates in series, withthe lamp L being shunted by the winding S in FIGURES 2 and 4, by thewinding S and P in FIGURE 1, and by the windings S and S in FIGURE 3.

While I have herein shown the present invention as applied to instantstart for cold cathode tubes, it is within the purview of the presentinvention to apply the principles thereof to hot cathode tubes byproviding a conventional heating circuit for the filaments of the tubes.

In FIGURE 5 I have shown one form of ballast that may be used inconnection with the present invention, this being one of the twoballasts shown in the Feinberg patent above referred to. In thisconstruction the ballast comprises a rectangular core 30 formed by astack of iron transformer laminations, and a similarly formed centralcore leg .31 on which the windings S P and S are located. The centralcore leg makes a snug fit with one end of the shell, as indicated at 33,and provides at the opposite end 34 a gap in the magnetic circuit, whichgap is bridged at 35, for reasons Well known in the art. The core 31)has magnetic shunts 10-10 which approach the central core member 31 andare spaced therefrom by air gaps 38-38. If desired shunts 10a10a(FIG. 1) similar to the shunts llti1(l may be provided between theprimary P and the secondary S The secondary S is of finer wire than isthe secondary S The secondary S may have of the order of four times asmany turns as the primary, whereas the secondary S may have a num-.

ber of turns two and one-half times that of the primary. This is merelyby way of example, as other relative ratios may be chosen depending uponwhich of the circuits are used, and depending upon the constants of thecircuits in accordance with known engineering principles.

In compliance with the requirements of the patent statutes I have hereshown and described a few preferred embodiments of my invention. It is,however, to be understood that the invention is not limited to theprecise constructions here shown, the same being merely illustrative ofthe principles of the invention. What I consider new and desire tosecure by Letters Patent is:

1. In combination, a pair of gaseous discharge devices, an alternatingcurrent supply for the devices comprising a three-windingauto-transformer having a primary, a loosely coupled first secondaryhaving one end connected with the said primary, a loosely coupled secondsecondary, the said first secondary having its second end connected withthe second secondary and in bucking voltage relationship to the secondsecondary, means including a capacitive reactor connecting one of saiddevices across the primary and the first secondary, means connecting thesecond of said devices across the primary and the first and secondsecondaries, and means for connecting the primary across a source ofalternating current, the secondaries having a turn relationship to theprimary to cause seriatim ignition of said first and second devices, andthe reactance of the first secondary being very high relative to thesecond secondary whereby after the said devices are both operating theapparatus will form in effect a series circuit including the devices,the capacitive reactor, and the second secondary.

2. In combination with two gaseous discharge devices, anauto-transformer having a primary, a loosely coupled high leakagereactance first secondary of more turns than the primary and connectedin step-up auto-transformer relationship with the primary, and a secondloosely coupled high leakage reactance secondary of more turns than theprimary but arranged in bucking relation thereto, said primary and saidfirst secondary and said second secondary being connected one after theother, means including a capacity reactor connecting one of said devicesacross the primary and only the first of the two secondaries, and meansconnecting the second of said devices across the primary and the twosecondaries.

3. In combination with two gaseous discharge devices, means foroperating the devices from a source of alternating current whose voltageis substantially less than the starting voltage of either of thedevices, said means including reactive means having a primary windingand first and second secondary windings loosely coupled to the primaryand to one another, the coupling of the first secondary winding beingsubstantially looser relative to the other two windings whereby toconstitute same a high leakage reactance winding, the windings beingconnected one after the other with the first secondary winding connectedbetween the other two windings, and the second secondary winding beingconnected in bucking voltage relationship to the first secondarywinding, a capacitive reactor having one side thereof connected to thecommon juncture of the secondaries, means connecting the first of saiddischarge devices between the second side of the capacitive reactor andthat end of the primary winding which is remote from the first secondaryand means connecting the second of said discharge devices across theprimary and both secondaries.

4. In combination, two instant start gaseous discharge devices, meansfor operating the same from an AC. source of voltage insuflicient toignite either device comprising an auto-transformer having a primary, afirst inductively reactive portion of said transformer of high leakageand of relationship relative to the primary for having a voltage inducedtherein greater than that of the primary voltage, a second inductivelyreactive portion of said transformer of high leakage and of relationshiprelative to the primary for having a voltage induced therein, means forimpressing the combined voltages of the primary and the said firstreactive portion across one of said devices for igniting same, meansconnecting the second discharge device across the primary and the tworeactive portions with the voltages of the two reactive portions inopposition to one another, said first portion producing after ignitionof the first device a voltage having a component in reverse relation tothe voltage across the first reactive portion prior to such ignitionwhereby it is additive relative to the voltage of the second reactiveportions, the sum of the primary voltage plus said component voltage andthe voltage of the second reactive portion being sufiicient to ignitethe second device.

5. A system comprising two instant start gaseous discharge devices, anauto-transformer supplying alternating current thereto said transformerhaving a primary, a loosely coupled first secondary having one sideconnected to one side of saidprimary and in additive voltagerelationship thereto, and a loosely coupled second secondary having oneside connected to the second side of said first secondary and in voltagebucking relationship to said primary, a capacitive reactor, one of saiddevices being connected across the primary and the first secondary andin series with the capacitive reactor and excluding the secondsecondary, the second of said devices being connected across the primaryand the two secondaries.

6. A system of the character described comprising an auto-transformerhaving a primary and two secondaries, the two secondaries being arrangedin voltage bucking relationship one to the other in a circuit containingboth secondaries, a capacitive reactor, a gaseous discharge device inseries with the reactor and connected across a part of the saidauto-transformer including at least a part of the primary and the firstsecondary and excluding the second secondary, a second gas dischargedevice connected across windings of said transformer including at leastboth of said secondaries and including at least a part of the primary,said windings and primary having a turn relationship to produce uponenergization of said primary a voltage across the first devicesufiicient to ignite the same, but across the second device insufficientto ignite the same, said first secondary having a high leakage reactanceand taking a lagging current upon initiation of the flow of currentthrough the first device whereby after ignition of said first devicethere will be a phase shift in the voltage thereof providing a componentadditive to the second secondary to increase the voltage across saidsecond device to a value suflicient to ignite the same.

No references cited.

